Art of dewaxing lubricating oils



Nov. 17,1'942.- E. M; us m1. 2,302,429

' ART OF DEWAXIRG' LUBRICATING OILS Fileddufie 15. .1940

HIGH MEL WAXY PARAFFINES POlNTr'AXES -&TO BE REJECTED Low MELTING POINT WAXES BORDER LINE PARAFFINES TO BE SEPARATED HIGH VISCOSITY INDEX ISOP ROPYL N'APHTHEN IC ACETATE UBRICATING OIL Low VISCOSITY INDEX ASPHALTIC COMPOUNDS DEWAXED SOLUTION INVENTOR. E. M. DQNS O. G. MAURO mm 2. m eww ATTORNEY.

Patented Nov. 17, 1942 i h'i'iilt'i' @FHCEZ ART OF DEWAXING LUERLICATING OILS Delaware Application June 15, 1940, Serial No. 340,670

6 Claims.

This invention relates to the art of dewaxing lubricating oils, and more particularly to the separation of paraifinic wax from parafiinic oil.

Prior to this invention, petroleum lubricating oils have been dewaxed to lower the pour points of the oils and at the same time recover the wax as a valuable product. An outstanding object has been to separate all of the oil from all of the wax and this has led to the use of selective solvents or combinations of solvents intended to dissolve all of the oil without dissolving the wax.

In this industry, the fundamental and theoretically ideal object has been to remove all of the wax without including valuable lubricating oil in the wax. However, after a great deal of research and experimental work extending over many years, the industry is still seeking a feasible real solution of this fundamental problem. In some cases, misleading results appear in very large yields of oil, but such yields are likely to include a substantial percentage of wax. In other cases, absolutely wax-free oil' has been obtained while a very valuable fraction of the original oil has been unexpectedly or unknowingly discarded in the wax.

Gur study of this problem has shown that it is not actually solved by merely removing all of the wax, as this result can be readily accomplished while discarding some of the oil with the wax. On the other hand, the problem is not solved by merely removing all of the oil, while retaining a substantial portion of the wax in the oil. Nevertheless, these false indications of success merely add confusion to the real problem, and tend to retard continued efforts toward a real solution.

Our investigations have shown that the most aggravating phase of the real problem appears in the border line between the low melting point p'arafinio waxes and the most valuable parafiinic oil. At this border line we find paraffinic oils and parafiinic waxes, the parafiines being so similar that the ordinary dewaxing solvents will not separate the border line oil from the border a-f'raction of the highest paraffinicity, having the highest viscosity index and, therefore, the most valuable portion of the oil.

An object of the present invention is to produce a dewaxing process wherein the dewaxing solvent will selectively dissolve not only the usual aromatic, naphthenic and paraffinic oils, but also the most valuable parafi'lnic border line oil, while rejecting the border line wax.

A further object is to obtain this result in an entirely feasible commercial process lacking the disadvantages likely to arise in one or more stages of such processes. More specifically stated, the process herein disclosed does not involve a critical rate of chilling, so we can obtain the advantage of rapid chilling or shock chilling, with-v out requiring special attention to this phase of the process, and the wax crystals can be veryreadily separated from the oil solution. The filter rate is very'high due to the low viscosity of the solution, and the entire process can be economically carried out in a very simple routine manner.

Another very important advantage appears in the flexibility or universality of the process. It

can be advantageously employed to dewax all of the usual lubricating oils, including oils within the extreme Viscosity ranges, and high or low paraffinic or naphthenic content, thereby pro viding a simple single system adapted for use in dewaxing the various lubricating distillates and residues. This eliminates the necessity of employing more than one system to efiiciently de-- wax the various oils in arefinery, and the advantages extend to the different petroleum oils from the widely separated fields including Mid- Continent, Gulf and Pennsylvania oils.

With the foregoing and other objects in view, the invention comprises the novel process hereinafter more specifically described and shown in theaccompanying drawing, which illustrates one form of the invention. However, it is to be understood that the invention comprehends changes, variations, and modifications within the scope of the claims hereunto appended.

Fig. l is a detail view illustrating various fractions of a body of oil, including the border line paraffines.

Fig. '2 is a. diagrammatical view of a simple system adapted for use in carrying out the new process.

The petroleum oil to be dewaxed may be either a distillate or a residue, and it may contain some or all of the constituents set forth in. Fig. 1.

However, the asphalticcompounds at the bot-1 tom of Fig. 1 are conveniently removed in a separate deasphalting process, and in cases where the ultimate product is a high viscosity index lubricating oil, the aromatic and naphthenic components may be removed in a separate extracting process, either before or after the dewaxing operation. However, the usual petroleum lubricating stock to be dewaxed will contain waxes of high and low melting points indicated at the upper portion of Fig. 1, and a paraffinic lubricating oil component, as well as some or all of the naphthenic and aromatic compounds.

Attention is now directed to the border line between the low melting point waxes and the paraffinic lubricating oil. Immediately above this line we find waxy parafiines in the low melting point wax, and immediately below said line we have liquid paraffines, or oil of the highest paraftinicity. This portion of the paraffinic oil has the highest viscosity index, and it is the most valuable part of the lubricating oil. However, it consists of paraffines similar to the paraflines in the low melting point wax, and the old dewaxing problem appears in selectively dissolving this oil of highest paraffinicity, without dissolving the similar parafiines in the Wax.

Briefly stated, the present invention involves the use of a combination of solvents which select and recover all, or a substantial part, of the border line parafiinic oil. This oil is separated from the border line wax and recovered in the body of dewaxed oil, thereby selectively separating approximately all of the desired lubricating oil from the wax content of the original oil. To accomplish this result we employ a combination of solvents, each having a low solvent power for Wax and relatively high solvent powers for the various paraifinic, naphthenic and aromatic oils.

In the preferred form of the invention, one of these solvents is isopropyl acetate, a very poor wax solvent but a good naphthenic oil solvent and a moderately good paraflinic oil solvent. The other selective solvent is methylene dichloride, a poor wax solvent, but a very good parafiinic oil solvent, and a moderately good naphthenic solvent. When either of these solvents is used alone, it would fail to accomplish the desired results, but when said solvents are combined with each other as hereinafter set forth, they provide the specific conditions necessary to first dissolve all of the constituents of the original oil, and thereafter selectively dissolve the oil fractions including approximately all of the border line paraffinic oil, without dissolving the similar paraifines in the border line wax. We believe that it is practically impossible to dissolve every trace of this border line oil without dissolving some of the wax, but Very substantial commercial advantages are gained by any improvement over the conventional industrial dewaxing operations, wherein the selective solvents fail to adequately control the selection of highly parafiinic oil at the border line. V

Fig. 2 is an illustration of a conventional dewaxing system adapted to carry out one form of the invention. In this View, 3 designates a storage tank for the oil to be dewaxed; 4 indicates a tank containing methylene dichloride, and 5 is a tank for isopropyl acetate. A stream of oil is pumped through a line 6 to a conductor 1, while streams of methylene dichloride and isopropyl acetate are pumped through lines 8 and 9, respectively, to a line In which leads to the conductor 1. The merged streams of solvents and oil may be transmitted to a heater 1 I and thence through a mixer l2 to a cooler or chiller I3 where the solution is chilled to precipitate the wax. The resultant chilled mixture may be transmitted through a line H to a receptacle l5 containing a rotary filter Hi. If this filter is of the vacuum type, the dewaxed oil solution passing through the filtering material will be discharged through a central pipe 11, while the wax will be deposited on the peripheral surface of the filter. This layer of wax may be removed at a stationary scraper l8 and discharged to a screw conveyor 19.

To very effectively wash oily solution from the layer of wax on the rotary filter l6, methylene dichloride alone may be pumped through a line 20 to a cooler 2i and thence to a spraying device 22 immediately above the filter. This methylene dichloride is preferably at a temperature substantially higher than the temperature of the wax. More specifically stated, if the solution is dewaxed at about 0 F. the temperature of the shower of methylene dichloride may be about 20 F., so as to very effectively dissolve and wash the oily solution from the layer of wax, the resultant solution being transmitted through the wax so as to enter into the dewaxed oil solution.

As a specific illustration, we will refer to the dewaxing of a reduced crude oil having a Saybolt Universal viscosity of 150 at 210 F., and using a solvent blend comprising 40 per cent isopropyl acetate and 60 per cent methylene dichloride. When employing about five volumes of this solvent blend to one volume of the oil charge, the dewaxing may be performed at about 15 F. to obtain a dewaxed oil having a pour point of about 10 F. to 15 F. About onehalf of a volume of methylene dichloride may be showered onto the layer of wax carried by the filter.

However, the proportions of the solvents may be varied as desired to meet different conditions. Oils of the highest parafiinicity require more methylene dichloride than oils of lower parafiinicity, and the viscosity of the oil is another factor in determining the proportions of methylene dichloride and isopropyl acetate. Iowever, indewaxing the various products, the isopropyl acetate preferably forms more than 25 per cent of the solvent blend, while the methylene dichloride is less than '75 per cent.

In the preferred form of the invention, the solution is heated to, for example, F., and then chilled to a temperature at Which the isopropyl acetate and methylene dichloride will selectively dissolve approximately all of the oil of highest parafiinicity without dissolving a substantial volume of similar parafiines in the wax component. The selected oil solution is then separated from the undissolved wax. The resultant product is a lubricatin oil having a low pour point, and a relatively high viscosity index due to the recovery of the most paraflinic oil which ordinarily remains with the similar waxy parafiines.

We claim:

1. In the art of dewaxing petroleum lubricating oil having paraflinic oil components and similar parafiinic wax components, the process of separating said similar parafiinic components which comprises dissolving said petroleum oil in a solvent comprising isopropyl acetate and methylene dichloride, chilling the solution to a temperature at which said solvent will selectively dissolve approximately all of the oil of highest paraflinicity without dissolving a substantial volume of similar parafiines in the wax component,

and separating the selected oil solution from the undissolved wax component.

2. In the art of making lubricating oil having a low pour point and a high viscosity index, the process of selecting and separating the paraffinic oil component of highest Viscosity index fro-m similar Daraffinic waxes which comprises dissolving a wax-bearin petroleum oil in a solvent comprising isopropyl acetate and methylene dichloride, chilling the solution to a temperature at which the isopropyl acetate and methylene dichloride will selectively dissolve approximately all of the oil of highest parafiinicity without dissolving a substantial volume of similar paraffines in the wax component, and separating the selected oil solution from the undissolved wax component.

3. In the art of dewaxing petroleum lubricating oil, the process of selecting and separating the most parafiinic lubricating oil from similar paraffines in low melting point paraflinic waxes which comprises dissolving the wax-bearing petroleum oil in a solvent comprising isopropyl acetate and methylene dichloride, chilling the solution to approximately a temperature at which said solvent will selectively dissolve substantially all of the paraifinic lubricating oil constituents without dissolving said similar paraffines in the low melting point parafiinic waxes, and separating the dissolved oil from the waxes.

4. In the art of dewaxing petroleum lubricating oil having aromatic, naphthenic and parafiinic oil components and a low melting point paraffinic wax component, the process of separating said paraffinic oil component from similar parafiines in the low melting point wax component which comprises dissolving said petroleum oil in a solvent comprising isopropyl acetate and methylene dichloride, chilling the solution to approximately a temperature at which the isopropyl acetate and methylene dichloride will selectively dissolve said oil components, including approximately all of the oil of highest parafiinicity, without dissolving similar parafilnes in the low melting point Wax component, and separating the selected oil solution from the wax.

5. In the art of separating petroleum oils and waxes, the process which comprises dissolving the oil and wax in a solvent comprising more than 25 per cent isopropyl acetate and less than '75 per cent methylene dichloride, cooling the solution to a temperature at which the isopropyl acetate and methylene dichloride will selectively dissolve the oil and reject the wax, and separating the selected oil solution from the rejected wax.

6. In the art of dewaxing petroleum lubricating oils, the process of deliberately separating unitary border line paraffines consisting of the most parafiinic lubricating oil constituents united with similar paraffines in low melting point waxes, said process including the steps of dissolving the wax-bearing oil in a solvent blend comprising isopropyl acetate combined with a predetermined quantity of methylene dichloride having a higher solvent power for parafiines, cooling the solution to a predetermined temperature, and separating the selected oil solution from the wax, said predetermined quantity of methylene dichloride being sufficient to cooperate with the isopropyl acetate in selectively dissolving substantially all of most paraflinic lubricating oil constituents without dissolving said similar paraffines in the low meltin point wax at said predetermined temperature, so as to positively separate said unitary border line paraffmes and at the same time transfer said most parafiinic oil constituents to the oil solution.

EDDIE M. DONS. OSWALD G. MAURO. 

